Optical vestibular stimulator

ABSTRACT

An apparatus to stimulate the vestibular system of an individual. The apparatus comprises an optical stimulator configured to optically stimulate a nerve area affecting a person&#39;s balance, and a control module coupled to the optical stimulator, the control module being configured to control the optical stimulator.

RELATED APPLICATION

This application is a continuation and claims the benefit of thepriority date of U.S. application Ser. No. 11/227,969, filed Sep. 14,2005, now U.S. Pat. No. 7,488,341, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

This invention relates to a medical prosthesis, and more particularly toa vestibular prosthesis.

BACKGROUND

The ability of human beings to maintain stability and balance iscontrolled by the vestibular system. This system provides the centralnervous system with the information needed to maintain balance andstability.

FIG. 1 is a diagram showing part of the vestibular system 100. As shown,the vestibular system includes a set of ring-shaped tubes, referred toas the semicircular canals 102 a-c, that are filled with the endolymphfluid. The semicircular canals are formed by a membrane called themembranous labyrinth. Each of the semicircular canals 102 a-c isdisposed inside a hollow bony tube (not shown in the diagram) called thebony labyrinth that extends along the contours of the semicircularcanals. As further shown in FIG. 1, each semicircular canal 102 a-cterminates in an enlarged balloon-shaped section called the ampulla(marked 104 a-c in FIG. 1). Inside each ampulla is the cupula 106 a-c,on which hair cells are embedded. Generally, as the semicircular canals102 a-c rotate due to rotational motion of a head, the endolymph fluidinside the canal will lag behind the moving canals, and thus cause thehair cells on the cupula to bend and deform. The deformed hair cellsstimulate nerves attached to the hair cells, resulting in the generationof nerve signals that are sent to the central nervous system. Thesesignals are decoded to provide the central nervous system with motioninformation. The three canals are mutually orthogonal and togetherprovide information about rotation in all three spatial dimensions.

The other endorgans in the vestibular system are the otolith organs, theutricle and the saccule. These endorgans act as linear accelerometersand respond to both linear acceleration and gravity.

In response to the vestibular nerve impulses, the central nervous systemexperiences motion perception and controls the movement of variousmuscles thereby enabling the body to maintain its balance.

When some hair cells of peripheral vestibular system are damaged, butothers remain viable (as often happens in situations involving bilateralvestibular hypofunction), the central nervous system of a personreceives inaccurate information regarding the person's motion. As aresult, the person's ability to maintain stability and balance will becompromised. Persons with improperly functioning vestibular systems mayconsequently experience vertigo, dizziness, and clumsiness, which maylead to collisions and spontaneous falls.

Another type of vestibular system affliction is Meniere's disease.Meniere's disease is a medical condition in which the vestibular system,for unknown reasons, suddenly begins varying the pulse-repetitionfrequency of the vestibular signal, even when the patient is stationary.This results in severe dizziness. Subsequently, and again for no knownreason, the vestibular system begins generating a vestibular signalconsistent with the person's spatial orientation, thereby ending theperson's symptoms.

One way to remedy symptoms associated with ailments that result in thecentral nervous system receiving inaccurate motion information is to useprostheses based on electrical stimulation. Such prostheses useimplanted or non-implanted transmitting electrodes to cause electricalstimulation of a target nerve (e.g., vestibular nerve ganglion cells).Such electrical stimulation results, for example, in correspondingreflexive responses in the vestibulo-ocular and the vestibulo-spinalpathways, thereby enabling the person to maintain balance and stabilityin response to the electrical stimulation. Alternatively, suchelectrodes can target nerves other than those associated with thevestibular system.

Similarly, to alleviate symptoms of Meniere's disease, electricalprostheses can be used to provide a stationary signal to the brain. Thiscan be achieved by producing a jamming signal, through electricalstimulation, that, when combined with a non-stationary signal present onthe vestibular nerve, causes the vestibular nerve to provide astationary signal to the brain. A description of the use of electrical,mechanical, and chemical stimulation of the vestibular system toalleviate Meniere's disease symptoms is provided in U.S. patentapplication Ser. No. 10/738,920, entitled “Vestibular Stimulator”, filedDec. 16, 2003, the contents of which are hereby incorporated herein byreference in their entirety.

Although useful in providing some relief from vestibular systemafflictions, electrical stimulation tends to affect large nerve areas.Such stimulation, therefore, is less useful when refined or focusedstimulation is sought. Moreover, electrical stimulation is generallyperformed using electrodes that have to be positioned proximate to thenerves that those electrode will target. Consequently, when the targetnerves are the nerves of the vestibular system, the electrodes have tobe surgically implanted close to those nerves. Such a surgical procedureoften necessitates cutting through bones surrounding the target nerves,thus resulting in considerable collateral damage to the affected area.

SUMMARY

In one aspect, the invention includes an apparatus to stimulate thevestibular system of an individual. The apparatus comprises an opticalstimulator configured to optically stimulate a nerve area affecting aperson's balance, and a control module coupled to the opticalstimulator, the control module being configured to control the opticalstimulator.

In some embodiments the control module is configured to control theoptical stimulator by generating a control signal for transmission tothe optical stimulator.

In some embodiments, the optical stimulator comprises an optical sourceconfigured to generate optical illumination, and an optical fibercoupled to the optical source and disposed proximate to the nerve area.In some embodiments, the optical source includes a laser device.

In some embodiments, the control module controls the optical stimulatorin response to motion information indicative of the person's motion. Insome embodiments the control module comprises a sensing system thatprovides the motion information indicative of the person's motion to thecontrol module.

In some embodiments, the control module is configured to provide ajamming signal that causes the optical stimulator to generate opticalillumination that stimulates the generation of stationary nerve signalstransmitted to the brain. In some embodiments the control module isconfigured to generate the jamming signal in response to anon-stationary signal detected by a sensor positioned proximate theperson's vestibular system.

In some embodiments the apparatus further comprises a power sourceelectrically coupled to the stimulator to power the stimulator.

In another aspect, the invention includes a method for stimulating thevestibular system. The method comprises directing light to stimulatenerve areas affecting a person's balance, and controlling the generationof the light.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of part of the vestibular system.

FIG. 2 is a schematic diagram of an embodiment of a vestibularstimulation apparatus.

FIG. 3 is a schematic diagram showing the optical stimulator of theapparatus of FIG. 2 disposed about the part of the vestibular systemshown in FIG. 1.

FIG. 4 is a translation sensor for use with the apparatus of FIG. 2.

FIG. 5 is a plan view of a rotation sensor for use with the apparatus ofFIG. 2.

FIG. 6 is a cross-sectional view of the rotation sensor of FIG. 5.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 2 is a schematic diagram of a vestibular stimulation apparatus 200to chronically stimulate a person's vestibular system. The apparatus 200includes an optical stimulator 210 inserted so that optical illuminationfrom the stimulator 210 can be directed at the vestibular nerves. Aswill be discussed in greater detail below, the optical stimulator 210 isconnected to a control module 220 that controls the optical modulationof the optical stimulator 210, and a power source 230 that powers theoptical stimulator 210. The control module includes the sensing system222, and the computing device 224.

As was reported in the paper “Optical stimulation of neural tissue invivo” by J. Wells et al. (OPTICS LETTERS/Vol. 30, No. 5/Mar. 1, 2005),neural tissue, including peripheral nerves, may be stimulated usingoptical radiation. While the exact mechanism that causes neural tissueto be stimulated using optical radiation is not fully understood at thispoint, it has been hypothesized that optical stimulation causeslaser-induced temperature increases. Such transient increases of thetissue temperature possibly trigger the activation of transmembrane ionchannels. This activates the neurons by eliciting action potentials,which are the means by which neurons transmit information to the brain.

FIG. 3 is an exemplary embodiment of the optical stimulator 210 disposedabout a portion of vestibular system. The optical stimulator 210includes an optical source 320 that generates the optical radiation thatis used to stimulate the nerves of the vestibular system. The particularoptical source 320 shown generates optical radiation in a wavelengthrange of 2-10 μm. Other optical ranges may also be used. The specificwavelength chosen depends on the type of the nerve tissue that is to bestimulated. The wavelength chosen must be one that can cause stimulationof the nerve tissue without damaging that nerve tissue. A usefulindicator of suitable wavelengths for achieving damage-free stimulationis the safety-ratio, defined as the ratio of the ablation threshold ofradiant exposure and the exposure power needed to stimulate the nerve.The ablation threshold is defined as the point at which the absorbedoptical energy is sufficient to break the bonds between molecules of thematerial absorbing it. Thus, high safety ratios are indicative ofsuitable optical wavelength. Empirical data suggests that suitableoptical wavelengths to stimulate the nerves of the vestibular system are2.1 μm and 4 μm.

An optical source that generates optical radiation having a wavelengthof 2.1 μm is a holmium:YAG laser. At that wavelength, the averagestimulation threshold for neural nerves is 0.32 J/cm², whereas theassociated ablation threshold is 2.0 J/cm². Thus, at a wavelength of 2.1μm, the safety ratio is approximately 6.25, which enables efficientstimulation of the neural nerves using laser illumination withoutdamaging them. Other lasers generating optical radiation at thatwavelength, or other suitable wavelengths may also be used. For example,white-light generators fitted with variable-length optical filters maybe used to generate optical radiation of particular wavelengths.

The optical source 320 may be placed outside the body, preferably atsome inconspicuous and unobtrusive location around the head of theindividual wearer, for example, behind the individual's ear.Alternatively, the optical source 320 may be placed at other locationson the body. Preferably, however, the optical source should be placed toavoid propagating optical radiation for distances that result insignificant optical power attenuation en route to the vestibular system.The optical source 320 may, in some embodiments, comprise severalindependent optical sources, such as separate laser sources, eachindependently provides optical stimulation to separate nerve areas ofthe vestibular system.

In some embodiments, the optical source 320 is internally placedproximate the vestibular system. For example, laser diodes, and otherphoton generating devices that are small enough to be implanted in theinterior of the head proximate to the vestibular system, may be used.

Because optical radiation is highly focused, the optical illuminationthat irradiates a vestibular nerve will generally affect a relativelysmall localized area of that vestibular nerve. Accordingly, toefficiently stimulate the vestibular system, it is necessary toseparately irradiate several nerve areas in the vestibular system. Asshown in FIG. 3, to stimulate a plurality of nerve areas affecting thecentral nervous system's ability to maintain a person's balance, theoptical radiation generated by the optical source 320 is directed viaoptical fibers 322 a-f to various locations in the part of thevestibular system shown in FIG. 3. Although six optical fibers are shownin the figure, additional optical fibers may be used.

For example, optical fiber 322 d is shown disposed proximate the cupula106 b in the ampulla 104 b, and is thus configured to illuminate, andthereby stimulate, the nerve endings in the cupula 106 b. Other opticalfibers are disposed proximate to other areas in the vestibular system inwhich vestibular nerve endings are bundled. The illuminated nerve areasinclude not only the nerves connected to the hair cells in the variouscupulas of the vestibular system 100, but also nerve areas at thevestibular system's other sensing organs, such as the otolith organs.Further, optical fibers may be disposed in other areas of the body todirectly illuminate nerves connected to the motion processing part ofthe central nervous system, like the vestibular nuclei orvestibulo-cerebellum.

Alternatively, rather than having fiber optics transmit opticalradiation generated by an optical source 320, individual implantedoptical sources, such as laser diodes may be directly disposed in andaround the nerve areas of the vestibular system 100.

In FIG. 3, the optical fibers extend subcutaneously from an interfacecoupling the optical source 320 to the optical fibers, to their variouslocations in and around the vestibular system. Accordingly, the opticalfibers 322 a-f are constructed from bio-compatible materials. Forexample, bio-compatible glass materials may be used to construct opticalfibers. Alternatively, fibers 322 a-f can be coated with layers ofbio-compatible materials like Teflon or silicone. Other suitablebio-compatible materials include metallic materials such as stainlesssteel or titanium, or various types of ceramics that are approved formedical applications. As a further alternative, the optical fibers 322a-f may extend within subcutaneous catheters that shield the opticalfibers 322 a-f from body fluids and tissues.

The use of optical fibers reduces the infliction of body trauma duringsurgical insertion. Because optical stimulation tends to be more focusedthan, for example, electrical stimulation, and can also propagatethrough translucent media (i.e., media that are partially, but notcompletely opaque), optical fibers may, in some circumstances, be placedopposite vestibular nerve areas surrounded by a translucent orsemi-opaque barriers without having to breach that barrier. For example,nerves emerging from the bony shell en route to the brainstem may bedirectly illuminated with optical illumination without having to breachany bony barrier. Further, even where vestibular nerves are surroundedby a bone, such as the bony labyrinth, optical radiation can propagatethrough the bony tissue and reach the nerves if the bone is sufficientlythin. Thus, in some locations in the vestibular systems, placement ofthe fiber optics near vestibular nerves surrounded by a bone would, atmost, require that the bone be thinned. There would be no need toactually cut or otherwise breach the bone. Accordingly, the use ofoptical stimulation can reduce the risk of damage to the vestibularsystem.

The optical fibers 322 a-f thus carry optical illumination from anoptical source 320. The level of optical illumination transmitted fromthe optical source 320 through each of the optical fibers 322 a-f (i.e.,the illumination power amplitude), as well as the illumination durationand/or frequency, is determined according to the control mechanism 220(in FIG. 2) that modulates the generation of optical illumination by theoptical source 320. Control signals generated by the control module 220are transmitted to the optical stimulator 210.

Specifically, if the optical stimulator 210 is to be used to conveymotion information to the vestibular system, the amplitude, frequencyand/or duration of optical illumination transmitted through each opticalfiber and projected onto the target nerve areas will depend on thelinear and rotational displacement of the person's head. Thus, forexample, if a person's head experiences a particular angularacceleration over a particular time, the amplitude level, frequencyand/or duration of the optical illumination transmitted through thoseoptical fibers disposed proximate to the corresponding cupulas will becommensurate with the rotation of the head.

On the other hand, if the optical stimulator 210 is to be used tocounteract the symptoms of Meniere's disease, the amplitude level,frequency, and/or duration of the optical illumination will be such thatresultant stimulated stationary nerve signals will be delivered to thecentral nervous system.

The control module 220 includes a motion sensing system 222 thatdetermines the person's movement, including rotation, translation,and/or orientation with respect to gravity. Data regarding a person'smotion is used to modulate the optical stimulation that provides thecentral nervous system with motion information. Examples of a motionsensing system are provided in U.S. Pat. No. 6,546,291, entitled“Balance Prosthesis,” the contents of which are hereby incorporated byreference in their entirety.

Generally, the motion sensing system 222 used to determine motioninformation for individuals having a damaged vestibular system includestranslation sensors and rotational sensors. These sensors typicallyinclude three translation sensors configured to sense the person'stranslation along the three coordinate axes and/or three rotationsensors configured to sense rotations along the three axes. An exemplarytranslation sensing device 400 is shown in FIG. 4. As shown, thetranslation sensing device 400 is a micro-mechanical device on which acantilevered beam 402 is mounted on a substrate 404. The beam 402suspends a proof mass 406 above a sense electrode 408. The proof mass406 and the sense electrode 408 together form a capacitor 410 having acapacitance that depends in part on the gap separating the proof mass406 from the sense electrode 408. An acceleration normal to thesubstrate 404 results in a force that deflects the proof mass 406 towardor away from the sense electrode 408, thereby changing the capacitance.This change in capacitance modulates a signal, which thus carriesinformation indicative of acceleration normal to the cantilevered beam402.

FIG. 5 is an exemplary rotation sensing device 500. As shown, therotation sensing device 500 is a micro-mechanical device that includes atuning fork 502 having first and second parallel tines 504 a, 504 bconnected to a base 506. A line extending through the base 506 andparallel to the first and second tines 504 a, 504 b defines a centralaxis 508 of the tuning fork 502. The first and second tines 504 a, 504 bof the tuning fork 502, when the tuning fork 502 is in its equilibriumposition, define an equilibrium plane. First and second proof masses 510a, 510 b are integrated onto the ends of the first and second tines 504a, 504 b respectively.

The rotation sensor 500 also includes an inner comb 512 disposed betweenthe first and second proof masses 510 a, 510 b. The inner comb has twosets of teeth 514 a, 514 b, each of which extends away from the centralaxis 508 in the equilibrium plane. Each proof mass 510 a, 510 b includesa plurality of inner teeth 516 a, 516 b extending toward the centralaxis in the equilibrium plane. These inner teeth 516 a, 516 binterdigitate with the corresponding teeth 514 a, 514 b extending fromthe inner comb 512.

The rotation sensor 500 also includes two outer combs 520 a, 520 b, eachdisposed adjacent to a proof mass 510 a, 510 b. Each outer comb 520 a,520 b has a plurality of teeth 522 a, 522 b extending inwardly towardthe central axis 508 in the equilibrium plane. Each proof mass 510 a,510 b includes a plurality of outer teeth 524 a, 524 b that extend awayfrom the central axis 508 in the equilibrium plane. These outer teeth524 a, 524 b interdigitate with the corresponding teeth 522 a, 522 b onthe outer combs 520 a, 520 b.

The proof masses 510 a, 510 b are suspended above first and second senseelectrodes 530 a, 530 b, as shown in the cross-section of FIG. 6. Eachproof mass 510 a, 510 b and its corresponding sense electrode 530 a, 530b thus defines a capacitor 540 a, 540 b having a capacitance thatdepends on the position of the proof mass 510 a, 510 b relative to thesense electrode 530 a, 530 b.

The inner and outer combs 512, 520 a, 520 b are connected to a voltagesource that generates a voltage on their respective teeth 514 a, 514 b,522 a, 522 b. This results in the generation of an electrostatic forcethat deflects the proof masses 510 a, 510 b in the equilibrium plane.The voltage on the teeth 514 a, 514 b, 522 a, 522 b of the inner andouter combs 512, 520 a, 520 b is selected to cause oscillation of theproof masses 510 a, 510 b in the equilibrium plane. To maintainoscillation, the rotation sensor consumes approximately 0.2 watts from a5 volt DC source. The oscillation of the proof masses 510 a, 510 bresults in the generation of an equilibrium angular momentum vector thatis perpendicular to the equilibrium plane and an equilibrium capacitancesignal measured at the sense electrodes 530 a, 530 b.

When the person wearing the rotation sensor 500 experiences a rotation,the angular momentum vector points in a different direction relative toa fixed reference frame associated with the wearers surroundings.Because angular momentum of the oscillating proof masses 510 a, 510 b isconserved, a torque is generated that causes the proof masses 510 a, 510b to oscillate above and below the equilibrium plane. This causes theangular momentum vector to recover its original direction.

As the proof masses 510 a, 510 b oscillate above and below theequilibrium plane, the capacitance of the capacitors 540 a, 540 bchanges. This change provides a signal indicative of rotational motionexperienced by the rotation sensor 500. The dynamic response of therotation sensor 500 has a bandwidth between 100 and 1000 Hz and amaximum rate range of 400 degrees per second.

It will be understood that other types of translation and rotationsensors having different configurations and designs may be used insteadof the translation and/or rotation sensors shown in FIG. 4 and FIGS. 5-6respectively.

Returning to FIG. 2, the motion sensing system 222, which includes oneor more sensing instruments such as a translation sensing device 400and/or rotation sensing device 500, is secured to the person's head,thereby enabling the sensing device to sense motion of the person'shead. The relatively small size of the sensing system 222 enablesplacement of the sensing system 222 on the external surface of the head,preferably at an inconspicuous and unobtrusive location. Alternatively,the sensing system 222 may be placed underneath the surface of the head,or at other locations on the person's body.

The control module 220 also includes a computing device 224. which canperform computations using digital and/or analog techniques. One of thefunctions the computing device 224 is configured to perform is toreceive data from the various sensing devices of the motion sensingsystem 222, to process the data, and to generate output controlinformation to be sent to the optical stimulator 210. Some operationsthat computing device 224 thus performs include filtering and scaling ofthe input motion data.

For example, sample streams from the rotation sensing devices employedby the motion sensing system 222 may be passed through integrators toobtain angular displacements. The outputs of the integrators can then bepassed through high-pass filters to remove low-frequency errorsintroduced by variations in the rotation sensors' bias voltages. Anotherprocessing operation that can be performed by the computing device 224includes passing motion data from the translation sensing devicesemployed by motion sensing system 222 through low-pass filters to removehigh-frequency contributions from the rotation sensing devices. Suitablelow-pass filters include third-order Butterworth filters having minus 3dB points near, for example, 0.03 Hz. The outputs of the high-passfilters that processed the rotational motion data and the low-passfilters that processed the translation motion data can then be passedthrough corresponding summers to obtain an estimate of the wearer'sorientation in an inertial coordinate system.

Other types of processing that the computing device 224 may beconfigured to perform can also include the implementation of a procedureto resolve the translation motion data into its various components todistinguish between acceleration that results in translation andacceleration caused by gravity. In particular, by using a pre-determinedinitial gravity vector g(0), and using the rotation data obtained fromthe rotation sensing devices, a rotation transformation can be performedto estimate the magnitude and direction of a gravity vector g(t) at anyinstant. This gravity vector can then be subtracted from the translationmotion data to derive the three linear translation motion vectors atthat instant due to linear acceleration corresponding to the actualtranslation of the wearer.

Another type of processing that may be performed by the computing device224 includes the determination of the person's orientation in aninertial coordinate system. For example, a Kalman filter thatincorporates a model of the dynamic characteristics of the motionsensing system 222 and of the person can be used to derive such anestimate. The resulting estimates from the computing device 224 can beprovided to an encoder for translation into a control signal that can beused to control the optical stimulator 210 and thereby stimulate theperson's vestibular system.

The control module 220 is also configured to provide a jamming signalwhen the stimulator apparatus is to be used for the purpose ofalleviating Meniere's diseases symptoms. In this case, the computingdevice 224 is configured to generate a jamming signal that is used tocause the optical source 320 to generate a properly modulated opticalsignal to stimulate the vestibular system to counteract the symptoms ofMeniere's disease.

The jamming signal characteristics are selected such that the resultingjamming signal causes the vestibular system to generate aconstant-repetition signal which in effect drowns out the time-varyingsignals produced by the malfunctioning vestibular system of the patientsuffering from Meniere's disease. One type of signal that can begenerated by the computing device 224 to modulate the generation ofoptical illumination by optical source 320 is a pulse train having acontrollable pulse amplitude and a pulse repetition frequency. Thesignal generated by computing device 224 thus causes the nerves of thevestibular system to generate a nerve signal having a constantpulse-repetition frequency. A time-varying signal of this type, thespectrum of which is substantially constant in time, is often referredto as a “stationary signal.” In one embodiment, the pulse-repetitionfrequency is approximately equal to the maximum neuron firing rate,which is typically on the order of 450 Hz. This pulse-repetitionfrequency is likely to result in the synchronous firing of neurons at ornear their maximum firing rate. However, it may be useful in some casesto have a much higher pulse-repetition frequency, for example in the1-10 kilohertz range, so that neurons fire asynchronously.

The jamming signal generated by the computing device 224 may cause theoptical source 320 of the optical stimulator 210 to produce other typeof time-varying jamming signals to stimulate the vestibular systemnerves. Examples of other jamming signals include sinusoidal signals orother oscillatory signals.

The jamming signal need only be on during an attack of Meniere'sdisease. When the attack subsides, the jamming signal is removed and thepatient regains normal vestibular function. The computing device 224thus includes a mechanism for applying and suspending the generation ofthe jamming signal.

For example, the computing device 224 has a patient-accessible switchlocated on a user interface (not shown) connected to the control module220. When the patient feels the onset of a Meniere's disease attack, heuses the switch to apply the jamming signal. A disadvantage of this typeof control unit is that because the jamming signal masks the symptoms ofthe attack, the patient is unable to tell whether the attack is over.Alternatively, the patient can simply use the switch to turn off thejamming signal after a reasonable time has elapsed. The resulting changein the pulse-repetition frequency of the signal received by the brainmay result in some dizziness. However, if the attack of Meniere'sdisease is in fact over, this dizziness should abate shortly. If thedizziness does not abate, the patient uses the switch to turn thejamming signal on again.

Alternatively, the signal suspension mechanism of the computing device224 can include a timer that automatically turns the jamming signal offafter the lapse of a pre-determined jamming interval. In someembodiments, the length of the jamming interval is user-controlled andcan be entered through the user interface, whereas in others, the lengthof the jamming interval is hard-wired into the control unit. If thedizziness does not fade after the jamming signal has been turned off,the patient uses the switch on the user interface to turn the jammingsignal on again.

In some embodiments, the computing device 224 includes an automaticcontrol unit having one or more sensors (not shown) that are implantedproximate to the vestibular system to measure the vestibular signal.When the control unit detects time-varying changes in thepulse-repetition frequency of the vestibular signal indicative of theonset of an episode of Meniere's disease, it causes the computing device224 to generate the jamming control signal that is transmitted to theoptical stimulator 210 to modulate the generation of opticalillumination. In this case, the jamming signal characteristics can bemade to vary in response to the characteristics of the measuredvestibular signal.

The resultant control signals sent to the optical stimulator 210 can beprovided continuously. For example, when signals corresponding to aperson's motion are transmitted to stimulator 210, the control signalcontinuously transmits information regarding the characteristics of theoptical illumination to be generated. Alternatively, the control signalssent to the optical stimulator 210 can be sent as short bursts separatedby pre-determined intervals (e.g., every 10 ms). Control signals sent asshort bursts can carry information regarding the level, duration and/orfrequency of the optical illumination. For example, based on a signallevel provided by the sensing device of the motion sensing system 222,the computing device 224 can determine a corresponding control feedbacksignal representing a discrete amplitude value, frequency value, and/ortime duration to be sent to the optical stimulator 210 to cause thecentral nervous system to properly stabilize and balance the person'sbody and/or head.

When the computing device 224 generates a constant jamming signal tocounteract the symptoms of Meniere's disease, the computing device 224can transmit a one-time signal that causes the optical source 320 of theoptical stimulator 210 to generate optical illumination at a constantrepetition rate, thereby stimulating the vestibular nerves to producenerve signals at a constant rate. When the symptoms of Meniere's diseasesubside, the computing device 224 can generate a signal that causes theoptical stimulator to suspend the generation of optical illumination.

Since the optical stimulator 210 includes one or more optical fibersconnected to the optical source 320, each of the optical fibers iscontrolled individually. This can be achieved by having the computingdevice 224 generate control signals that separately control the opticalillumination transmitted through each of the optical fibers 322 a-f.Alternatively, in embodiments having multiple optical sources, thecomputing device generates control signals that control each of theoptical sources of the optical stimulator 210.

If a single optical source 320 is used to generate optical illuminationat the various optical fibers, the control signals can be sent usingtime-division multiplexing. In this case, control signals to control thegeneration of optical illumination at each optical fiber 322 a-f aresent in sequence. Other methods for transmitting control signals fromcomputing device 224 to the optical stimulator 210 can also be used. Theoptical source 320 can use the control signals it receives from thecomputing device 224 to sequentially generate the optical illuminationto be transmitted through each of the optical fibers 322 a-f using asimilar time-division multiplexing scheme. Using such a scheme thusenables the optical stimulator 210 to independently control and generatethe optical stimulation at various nerve areas so that different nerveareas are exposed to different optical stimulation. Alternatively, theoptical source 320 can simultaneously generate the optical illuminationtransmitted through the optical fibers using, for example, a wavelengthdivision multiplexing scheme. Implementation of a wavelength divisionmultiplexing would require that the optical source be capable ofgenerating optical illumination at different wavelengths. Such a schemewould enable simultaneous independent control of the various opticalfibers 322 a-f. Alternatively, in some embodiments the optical source320 may provide the same level of optical illumination to each of theoptical fibers. Such embodiments may be particularly useful when theapparatus 200 is used to counteract Meniere's disease symptom by causingthe vestibular nerves to generate nerve signal at a constant repetitionrate, thereby effectively drowning out the non-stationary signalproduced by the patient's malfunctioning vestibular system.

The computing device 224 may include a computer and/or other types ofprocessor-based devices suitable for multiple applications. Such devicescan include volatile and non-volatile memory elements, and peripheraldevices to enable input/output functionality. Such peripheral devicesinclude, for example, a CD-ROM drive and/or floppy drive, or a networkconnection, for downloading software containing computer instructions toenable general operation of the processor-based device, and fordownloading software implementation programs to process input motiondata and generate corresponding control information to control thegeneration of optical illumination by an optical source, and/or togenerate control signals to control the generation of opticalillumination jamming signals. Additionally or alternatively, thecomputing device 224 may include a digital signal processor (DSP) toperform the various processing functions described above. A suitable DSPis the Analog Devices ADSP 2183 processor.

The computing device 224 is placed on the person's head proximate to thesensing system 222, thereby minimizing the distance that signals fromthe sensing devices have to travel to reach the computing device.However, the location of the computing device 224 is not critical. Thedevice 224 can thus be placed anywhere on or off the person's body.

As noted above, the control device 220 also includes a user interface(not shown) to enable direct control by a user (such as the personwearing the optical stimulator, a physician, or a technician) to controlthe generation of optical illumination by the optical source 320 of thestimulator 210. Input entered through the user interface is processed bythe computing device 224 to generate corresponding control signals forthe stimulator 210. Typical user interfaces include a small key pad toenable the user to enter data, and/or a switch for activating orsuspending the generation of a jamming signal. Such a key pad, and/orswitch, could be attached to a housing in which the computing device 224is held. However, the user interface need not be located proximate tothe computing device 224. For example, a computer console can beremotely linked to the computing device 224, either using wirelesstransmission, or by direct physical coupling. Executing on such acomputer console would be, for example, a graphical user interface toenable the user to enter the data for controlling the optical stimulator210.

FIG. 2 further shows that the optical stimulator also includes a powersource 230 to power, among other things, the sensing system 222 and/orthe stimulator 210. The power source 230 may be a battery carried orattached to the person. The power source 230 is electrically coupled tothe control module 220 and/or the optical stimulator 210 usingelectrical conducting wires. Alternatively, powering of the controlmodule 220 and the stimulator 210 may be implemented through powertelemetry, in which power is delivered to the stimulator 210 and/or thecontrol module 220 via wireless power transmission. In some embodimentsthe power source 230 may include several independent power units. Forexample, a battery for delivering sufficient power to the control module220 could be connected directly to the control module 220 via electricalwires. A separate power unit, situated at a different location, could beused, for example, to deliver power to the stimulator 210 using powertelemetry.

Typically, the apparatus 200 has to be calibrated. Calibration of theapparatus 200 can include calibrating the motion sensing system 222. Thesensors of the motion sensing system 222 are calibrated to establish therelationship between the output signals of the sensors (for instance,rotation sensors such as the sensor 500 shown in FIG. 5) and the actualtranslation and rotational motion undergone by the person wearing thestimulator 200. Once that relationship is determined and represented asa mathematical mapping or transformation in the form of, for example, amatrix, the output signals (typically electrical voltage levels) sensedat the various sensing devices of the sensing system 222 are forwardedto the computing device 224 of the control module 220. There, the analogsignals generated by the sensing devices are converted to digitalsignals using an analog-to-digital converter. Subsequently, themathematical transformation or mapping determined during the calibrationstage is applied to the digital signals to obtain a measure of themotion (rotational and/or translational) undergone by the person wearingthe apparatus 200.

Calibration of the motion sensing system 222 can also includecomputation of mathematical transformations, represented by matrices,that convert the signals measured by the various sensing devices of thesensing system 222 so that the transformed motion signals are orthogonalto each other. The transformation can also be designed to translate themotion signals measured in one coordinate system to another coordinatesystem more suitable for generating the control signals provided to theoptical stimulator 210.

Additionally, calibration of the apparatus 200 includes determiningfiltering to best provide the person's motion information. Parametersthat correlate the person's motion, as predicted by the model, with thecontrol feedback signals that are provided to the vestibular system aredetermined. As previously noted, the control feedback signals areencoded and transmitted to the optical stimulator 210, which then usesthem to control its optical stimulation of the vestibular system. Forexample, if a high-pass filter is used to encode rotational informationin a manner that mimics the normal dynamics of the canals and generatesa control feedback signal needed to obtain rotational stability of aperson's head, then the filter parameters would need to be determined.The determination of these parameters generally has to be performedconcurrently with the determination of the level of optical illuminationgenerated by the stimulator 210, as described below.

Calibration of the apparatus 200 also includes calibrating the level ofoptical illumination provided by the optical source 320 to each of theoptical fibers 322 a-f. Calibration of the level of optical illuminationby an optical source 320 is performed by examining the response of theperson to various levels of stimulation given controlled movement androtation of the person's body and/or head. For example, when the opticalstimulator 210 is used to stimulate the vestibular system to providecontrol information to the central nervous system, the person maypassively rotate or be asked to rotate his head towards a fixedpre-determined point in space. The level of optical illumination at eachof the optical fibers 322 a-f connected to the optical source 320, giventhe control feedback signal received from the computing device 224, isthen manually varied until the point at which the level and/or manner ofoptical illumination by the optical fibers 322 a-f enables the person toimprove stability and balance (e.g., until the illumination level atwhich the person no longer experiences some of the clinical symptoms ofinstability, like dizziness), or until a desired response is obtained.For example, one way to calibrate the optical stimulator 210 is bymonitoring the eye movements of the person in response to various levelsof illumination. Since one of the functions of the central nervoussystem is to control the movement of the eye to enable clear visionduring head motion, there is a strong correlation between stimulation ofthe vestibular system and movement of the eyes. Other ways to calibratethe stimulator 210 may also be used.

In operation, when the apparatus 200 is used to control the balance andstability of a person, sensing devices, such as the translation sensingdevice 400 and/or the rotation sensing device 500, mounted on the headof a person, sense rotational and translational motion of the headand/or body of the person. The sensing devices produce electricalsignals that are sent to the computing device 224 of the control module220. The computing device 224 processes the received signals to providevalues or signals indicative of the motion undergone by the person. Theprocessed signals are then used to produce control signals that areprovided to the optical stimulator 210. The optical source 320 of thestimulator 210 generates optical illumination for each of the opticalfibers 322 a-f connected thereto. The transmitted optical illuminationis then projected from the end of the respective optical fibers disposedproximate to various nerve areas, including nerve areas of thevestibular system.

When the apparatus 200 is used to produce jamming signals to counteractthe non-stationary signals transmitted by the nerves of the vestibularsystem of a person suffering from Meniere's disease, the computingdevice 224 generates signals to modulate the generation of opticalsignals. The generated optical signals stimulate the nerves of thevestibular system (and/or other nerve areas) to cause them to generatenerve signals at a constant repetition rate. Generation of controlsignals by the computing device 224 can be triggered automatically whena sensing device senses the onset of an attack of Meniere's disease, ormanually when the patient, or some other individual, operates a switchthat causes the computing device 224 to generate and transmit thecontrol signals to modulate the optical source 320.

Although FIG. 2 shows only a single stimulator 210, additional opticalstimulators may be used. For example, a companion optical stimulator(not shown in the figure) may be placed in the person's other ear. Useof such an additional stimulator would be particularly useful to providesymmetric stimulation to alleviate bilateral vestibular conditions thataffect a person's left and right vestibular organs (i.e., both ears).Further, use of multiple stimulators may also be desirable to moreaccurately mimic the complementary functioning of a person's bilateral(left and right side) peripheral vestibular organs. Further, the opticalstimulator 210 may be used in conjunction with other types ofstimulators and/or actuators. For example, the optical stimulatordescribe herein may be used with any of the mechanical actuatorsdescribed in U.S. patent application Ser. No. 11/193,034, entitled“Mechanical Vestibular Stimulator”, filed Jul. 29, 2005, the contents ofwhich are hereby incorporated herein by reference in their entirety,and/or with the various stimulators (e.g., electrical, mechanical, orchemical) described in U.S. patent application Ser. No. 10/738,920.

Further, although FIG. 2 shows the apparatus 200 being used with a humanbeing, the apparatus 200 can also be used with animals. The apparatus200 need not be used only to alleviate medical conditions affecting aperson's balance and stability, but can also be used for otherconditions in which stimulation of the vestibular system is required ordesirable. Further, the apparatus 200 may be used for non-therapeutic oreven non-medical purposes. For example, the apparatus 200 can be used inthe course of medical research to investigate the functioning of thebrain.

Other Embodiments

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. An apparatus to stimulate a vestibular system of an individual, theapparatus comprising: an optical stimulator configured to opticallystimulate a plurality of nerve areas affecting a person's balance, theoptical stimulator including an optical source configured to generateoptical illumination and a plurality of optical fibers, wherein eachoptical fiber is coupled to the optical source at a proximal end suchthat a distal end of the optical fiber can be placed proximate to one ofthe plurality of nerve areas; and a control module coupled to theoptical stimulator, wherein the control module is configured to causethe optical stimulator to simultaneously stimulate the plurality ofnerve areas, wherein the control module controls the optical stimulatorin response to motion information indicative of the person's motion. 2.The apparatus of claim 1, wherein the control module is configured tocontrol the optical stimulator by generating a control signal fortransmission to the optical stimulator.
 3. The apparatus of claim 1,wherein the optical source comprises a laser device.
 4. The apparatus ofclaim 1, further comprising a sensing system that provides the motioninformation indicative of the person's motion to the control module. 5.The apparatus of claim 1, further comprising a power source electricallycoupled to the stimulator to power the stimulator.
 6. The apparatus ofclaim 1, wherein the optical stimulator is configured to be implanted inthe person.
 7. The apparatus of claim 1, wherein the optical sourcecomprises several independent sources each independently providingoptical stimulation to separate nerve areas of the vestibular system. 8.An apparatus to stimulate a vestibular system of an individual, theapparatus comprising: an optical stimulator configured to opticallystimulate a plurality of nerve areas affecting a person's balance, theoptical stimulator including an optical source configured to generateoptical illumination and a plurality of optical fibers, wherein eachoptical fiber is coupled to the optical source at a proximal end suchthat a distal end of the optical fiber can be placed proximate to one ofthe plurality of nerve areas; and a control module coupled to theoptical stimulator, wherein the control module is configured to causethe optical stimulator to simultaneously stimulate the plurality ofnerve areas, wherein the control module is configured to provide ajamming signal that causes the optical stimulator to generate opticalillumination that stimulates generation of stationary nerve signalstransmitted to the brain.
 9. The apparatus of claim 8, wherein thecontrol module is configured to generate the jamming signal in responseto a non-stationary signal detected by a sensor positioned proximate thevestibular system.
 10. The apparatus of claim 8, further comprising apower source electrically coupled to the stimulator to power thestimulator.
 11. The apparatus of claim 8, wherein the optical stimulatoris configured to be implanted in the person.
 12. The apparatus of claim8, wherein the optical source comprises several independent sources eachindependently providing optical stimulation to separate nerve areas ofthe vestibular system.